The present invention relates to a generator set consisting of a linear electric generator integrated with an internal combustion engine, a control method and a traction unit accomplished with it.
Known in the art are generator sets formed of an electric rotary generator driven by a normal internal combustion engine interconnected therewith. Bulkiness, weight and complexity of these sets is well known.
"Linear" generator sets have been proposed, which comprise an internal combustion engine made of two opposite piston-cylinder sets fixedly connected in phase opposition, between which a slide forming a linear-movement electric generator is disposed.
However, in the known art, either a movement of the slide at will or a movement having a sinusoidal speed profile has always been proposed. In the first case, each piston is very likely to hit the head of its own cylinder (or the safety end-of-stroke elements, if any) in case of failure in ignition or out-of-phase ignitions. In the second case, a sinusoidal course is conceived for the purpose of simulating the equivalent of a flywheel that in a normal internal combustion engine controls the piston acceleration and deceleration strokes. The flywheel effect is simulated by controlling the electric energy absorbed by the electric generator behaving like a generator, motor or electric brake depending on the current direction between the generator and the user or the storage means of the produced electric energy.
For example GB-A-2,219,671 discloses a linear generator in which a sinusoidal motion is imposed to the movable portion.
EP-A-0 120 986 describes a linear generator in which control of the generator movement is made for simulating a mass-free flywheel, by periodically feeding the generator like a motor.
As a result of experiments carried out by the herein applicant, the idea of an electric flywheel storing and giving back energy into and from the slide in order to cause a sinusoidal motion of same cannot be proposed due to the great amount of the exchanged energy with respect to the useful one. The Applicant has found that by a sinusoidal motion the electric generator would have to transfer great amounts of energy from and to the slide, in the form of kinetic energy, against a very reduced amount thereof drawn during a whole cycle. Under these conditions, a yield of the electric generator which is even slightly lower than the unit greatly impairs the overall yield, making it even null. It has therefore appeared that in this type of control it is impossible to leave out of consideration the energy extraction/admission yield in the mechanical system, which yield is typically in the order of 80-90% and invalidates any system taking into account the possibility of taking up and introducing kinetic energy from and into the mechanical system.
The basic error contained in wishing to impose a sinusoidal motion or leaving a free motion to the slide has hitherto prevented accomplishment of "linear" generator sets having such satisfactory performance that they could be used in a practical way.
It is a general object of the present invention to obviate the above mentioned drawbacks by providing a linear generator set having such a yield and operating safety that it can really be advantageously used for replacing traditional generator sets with a rotary internal combustion engine and electric generator. It is also provided an electric traction unit comprising this electric generator.